Chemical Mapping of the Milky Way with The Canada-France Imaging Survey: A Non-parametric Metallicity-Distance Decomposition of the Galaxy

We present the chemical distribution of the Milky Way, based on 2900deg2ofu-band photometry taken as part ofthe Canada–France Imaging Survey. When complete, this survey will cover 10,000deg2of the northern sky. Bycombing the CFHTu-band photometry together with Sloan Digital Sky Survey and Pan-STARRSgr,,andi,wedemonstrate that we are able to reliably measure the metallicities of individual stars to∼0.2dex, and henceadditionally obtain good photometric distance estimates. This survey thus permits the measurement of metallicitiesand distances of the dominant main-sequence(MS)population out to approximately30 kpc, and provides a muchhigher number of stars at large extraplanar distances than have been available from previous surveys. We develop anon-parametric distance–metallicity decomposition algorithm and apply it to the sky atb3070∣∣< <and to theNorth Galactic Cap. Wefind that the metallicity–distance distribution is well-represented by three populations whose metallicity distributions do not vary significantly with vertical height above the disk. As traced in MS stars,the stellar halo component shows a vertical density profile that is close to exponential, with a scale height of around3kpc. This may indicate that the inner halo was formed partly from disk stars ejected in an ancient minor merger.